SOMATOSENSORY CORTEX

Learning Objectives SOMATOSENSORY CORTEX Homunculus SOMATOSENSORY AREA I SOMATOSENSORY AREA II Somatosensory association area

Cerebral Cortex Brodmann’s areas Fifty Histological ---- Functional General Scheme –Central fissure –Sensory signals from all modalities - Posterior –Anterior half parietal Lobe – Somatosensory signals – Reception and Interpretation –Posterior half – Still higher levels of interpretation

Visual signals- Occipital Lobe Auditory signals - Temporal Lobe Posterior half of frontal Lobe Muscle contraction & Body movements Sensory signals from all modalities - Posterior Anterior half parietal Lobe – somatosensory signals – reception and interpretation

Somatosensory cortex SOMATOSENSORY AREA I Post central gyrus - cerebral cortex High degree of localization Extensive and more studied - more important Areas 3,1,2 SOMATOSENSORY AREA II Poor localization Less studied Signals enters here: –From brainstem –From somatosensory cortex –From visual area –From auditory area

Receive information from opposite side of body

Structural layers of cerebral cortex I Molecular II Ext Granular III Small Pyramidal cells IV Int Granular cells V Large Pyramidal Cells VI Fusiform/Polymorphic cells layer

Incoming signal excite neuronal Layer IV Layers I and II receive diffuse, nonspecific input signals from lower brain centers The neurons in Layers II and III send axons - the cerebral cortex Layer V - Generally larger and project to more distant areas, such as to the basal ganglia, brain stem and spinal cord. Layer VI, especially large numbers of axons extend to the thalamus, providing signals from the cerebral cortex

Functions of somatosensory area I 1.Localize discretely - different sensations 2.Critical degrees of pressure 3.Weights of objects 4.Shape or form of objects -- Stereognosis 5.Texture of objects 6.Localize pain and temperature sensations

Somatosensory association area Brodmann’s area 5 and 7 Parietal cortex - behind somatosensory area I Decipher sensory information entering somatosensory area I Receives signals from: –Somatosensory area I –Ventrobasal nuclei of thalamus –Other nuclei of thalamus –Visual and auditory cortices

Effect of removing somatosensory association area  Unable to recognize complex objects/complex forms by feeling them on opposite side  Loses sense of form of his/her own body / body parts on opposite side  Oblivious to opposite side  Forgets to use opposite side for motor functions  Tends to recognize one side of object and forgets other side - Amorphosynthesis